This proposal covers a program of comparative research on the development of infant attachments in monkeys, and is based on a series of data and hypothesis from the child and primate literature. The study using a balanced design will test the interacting effects of three antecedent conditions, i.e., species, sex of infant and complexity of rearing environment on an integrated array of developmental measures relating to attachment and the presumably coordinated development of "object-permanence". The two species to be studied, will be bonnet (M. radiata) and pigtail (M. nemestrina) macaques. The rearing environments will be: isolate mother-infant dyads, paired dyads, and group living dyads. The measures to be taken will focus on: dyadic interactions in Home Cage Observations; the discrimination of mother and response to familiar and strange females in a new test, the Mother-Stranger Preference Test; the emergence of an "object-permanence", both with regard to responses to mother and towards a familiar toy, to be assessed in a new apparatus and two tests, the Primate-Permanence and Inanimate-Object Permanence Tests; the developmental changes in response to brief separations from mother; and, the response to prolonged separation from mother at approximately five and nine months of life.